From the moment portrait artist Ralph Wolfe Cowan clapped eyes on the young man, he knew that he would have to paint him. The potential subject was tall, slim and dressed in street clothes-dark yellow madras shorts, a pale yellow pullover and dirty sneakers. He was not, however, the sort who would remain still for a sitting at Cowan's West Palm Beach, Fla., studio. In fact, when the artist last saw the guy, he was dashing from a darkened parking lot, clutching Cowan's gold neck chain.

Ordinarily, Cowan, 57, doesn't seek commissions from anonymous young muggers; his clientele is limited to the rich, the famous or both. The Sultan of Brunei recently paid Cowan $600,000 for a series of family portraits. Cowan has rendered the likenesses of such luminaries as JFK, Princess Grace and her family and Pope John Paul II—and his portrait of Elvis hangs in Graceland.

But on the night of July 10, in a fast-food parking lot not far from his home, Cowan's career took an unexpected turn. "The man just reached through the open car window, ripped the chain off my neck and disappeared into the night," says Cowan. "I immediately flagged a cop across the street who searched the area but couldn't find him."

The mugger, of course, couldn't have known that Cowan was a portrait painter. "If anyone attacks me, they better hide forever because I have a photographic memory," Cowan says. "I can duplicate after a split second." He went home and promptly sketched the thief's face. The next morning he expanded the work into a 24-by 30-inch portrait in oils, with the mugger still clutching the snatched 18-karat gold scarab and chain. As a final flourish, Cowan signed his work, which he now values at $7,500.

The West Palm Beach police were duly impressed. "I have never seen anyone go to this extreme," said Detective Jack Yates. "People have come in with sketches, but this is the first time anyone ever brought in a portrait with such clarity." The cops photographed the portrait for wanted posters. At last report, however, the perpetrator was still at large.

Cowan, meanwhile, has reclaimed his painting and taken it home for safekeeping. He feels that it remains incomplete. "The real fun will come," he says with anticipated glee, "when I can paint some bars in front of my assailant's face."